The present invention relates to a one-way clutch for a reduction-geared motor which drives an anchor of a passive seat belt, a power window, a sunroof for an automotive vehicle and so on.
For example, the anchor, the power window, and the sunroof moves under the effect of an external force during stopping of the reduction-geared motor, which is undesirable for the reduction-geared motor with a view to securing passenger's safety and preventing crime. Therefore, a worm gear has been used as reduction means in order to prevent the driving motor from being rotated by the external force acting on driven articles, that is, in order to prevent a reverse driving when the motor is stopped.
However, a lead angle at a pitch point must be narrowed so that the worm gear can perform the function of preventing the reverse driving. If the lead angle at the pitch point is adapted to be narrow, a large loss is generated by sliding between tooth surfaces at a meshing portion thereof, which causes a tendency for a low rotation transmission efficiency. Further, pressure gets high between the tooth surfaces, and a worm wheel of the worm gear often was damaged when the driven articles were shocked suddenly, for example, when the seat belt was shocked suddenly in emergency.
Lately, a demand for a large passenger compartment causes pillar, door and ceiling of the vehicle to be limited in thickness and requires the reduction-geared motor disposed therein to be small and thin. In order to make the reduction-geared motor small and thin, using a worm gear having a wide lead angle at the pitch point, or gears other than the worm gear, such as a spur gear and a bevel gear, the rotation transmission efficiency should preferably be heightened. However, these gears have no function of preventing reverse driving. This made it necessary for the above gears to have a locking mechanism outside the reduction-geared motor so as to prevent reverse driving. Referring to FIG. 6, there is shown the reduction-geared motor for driving the anchor of the passive seat belt as an example of a conventional reduction-geared motor.
An output shaft 2 which drives the anchor (64 in FIG. 4) is supported in a gear casing 8. A cover 12 of the casing 8 is screwed on a casing body 10. A worm wheel 6 meshes with a worm 4 formed in a shaft of an electric motor 3. The worm 4 widens the lead angle at the pitch point in order to heighten the rotation transmission efficiency. The worm 4 can be driven reversely by about 45 kg.cm of rotary driving force on the worm wheel 6 side. The worm wheel 6 is supported in the output shaft 2. A rubber plate 34 is secured between a first disc 32 and a second disc 35 to form a cushion rubber member 30. A projection 40 is formed in the first disc 32 and engages with an engagement hole 31 provided in the worm wheel 6. A substantially-oval hole 44 is made in the center of the second disc 35. The diameter of the output shaft 2 is reduced in two stages in a lower portion of the shaft for supporting the worm wheel 6. A first reduced-diameter portion 18 has a parallel-cut portion 20 with a substantially-oval section and an annular groove 22 beneath the parallel-cut portion 20. The hole 44 of the second disc 35 engages the first reduced-diameter portion 18 and a snap ring 46 causes the second disc 35 not to move in an axial direction.
Consequently, a rotary driving force of the electric motor 3 is transmitted to the output shaft 2 via the worm 4, the worm wheel 6 and the cushion rubber member 30.
While a seat belt is fastened to a passenger, the locking mechanism (not illustrated) provided outside the reduction-geared motor fixes the anchor of the seat belt and burdens the sudden shock in emergency.
The conventional reduction-geared motor requires the locking mechanism to be provided in the outside thereof in order to secure passenger's safety and prevent crime. Locating the locking mechanism outside the motor, however, is disadvantageous because the passenger compartment gets small.
Meanwhile, the manual operation requires the locking mechanism to be disengaged once. If the locking mechanism cannot be disengaged, for example, when the locking mechanism breaks down, there was a further disadvantage in that manual operation cannot be performed.